During cardiac arrest, it is desirable to generate blood flow by external means in order to maintain brain and heart viability. Traditionally, the external means of generating blood flow has been manual cardiopulmonary resuscitation (CPR). Using CPR, the rescuer tilts the patient's head back, lifts the chin to clear and straighten the airway, and depresses the sternum 11/2 to 2 inches 15 times (at a rate of 80 to 100 depressions per minute), after which the rescuer gives the patient 2 full breaths. This 15 depressions and 2 breaths is repeated cyclically.
Currently, the CPR research community believes that blood flow produced by external means can be explained by one, or a combination of two, theoretical mechanisms: the "cardiac pump" mechanism and the "thoracic pump" mechanism.
According to the cardiac pump mechanism, blood flow caused by external means is due to direct mechanical compression of the heart. During compression, blood is squeezed out of the heart chambers, and during release of the compression (relaxation) blood flows into the heart chambers. Backflow of the blood is prevented by the valving of the heart and vessels.
According to the thoracic pump mechanism, blood is pumped by external means as a result of the cyclical increase and decrease of intrathoracic pressure. During compression, the intrathoracic pressure rises, which causes blood to be forced out of the blood vessels and organs located in the thorax, and the blood flows into the peripheral tissues. During release, blood flows back into the thorax via the normal venous return. In this method, backflow is prevented by the valving of the veins.
Most researchers believe that both mechanisms are active to some degree However, the methods presently in use, and the devices currently in use, for promoting blood flow by the application of an external force are directed toward only one of the two mechanisms. In order to maximize blood flow, a device which takes advantage of both mechanisms is needed.
A variety of devices have been developed to increase blood and/or air flow in the chest cavity of a cardiac arrest patient.
U.S. Pat. No. 2,071,215 to Petersen shows a piston and cylinder arrangement attached to two ends of a girdle which encircles a patient's chest. The expansion or compression of a fluid in the piston and cylinder combination tightens and loosens the girdle to ventilate the lungs. This device is large and heavy, and is dependent upon a compressed fluid for driving power.
U.S. Pat. No. 3,425,409 to Isaacson et al. discloses an apparatus for compressing the sternum by a downward force generated by a piston. A belt is placed around the chest in order to minimize bodily damage, and air is applied to the air passages of the patient.
U.S. Pat. No. 5,287,846 to Capjon et al. shows an upper frame that rests on a patient, whose back rests on a lower frame. Retractable straps extend from the upper frame and attach to the lower frame. A hydraulic cylinder in the upper frame presses downwardly on the chest.
Barkalow, in U.S. Pat. No. 3,461,860, discloses a device using a pneumatic plunger to mechanically compress the sternum a predetermined distance. A mechanical ventilator was added to this device in U.S. Pat. No. 4,326,507 to insure proper ventilation and increase the volume of the chest. This device was limited in its success due to complexity which requires trained personnel to use it.
A similar device was disclosed in U.S. Pat. No. 4,060,079 to Reinhold, This device is merely a similar portable unit.
Bloom, in U.S. Pat. No. 4,338,924, shows a sternum compression device using an air cylinder to depress the chest of the cardiac arrest patient. This device, like many others using a chest compression design, is large and heavy.
Newman et al., in U.S. Pat. No. 4,424,806, show a pneumatic vest for generating a rise in thoracic pressure. This vest uses the "thoracic pump" concept of exerting greater force over a larger area under the assumption that if more major organs could be compressed and released, greater blood flow would occur. By releasing the compression force, the chest would return to its normal size and draw blood back into the major organs. Positive blood flow would occur due to the one-way valves in the vascular network. The Newman device is not readily portable, in addition to having substantial complexity. In U.S. Pat. No. 4,928,674, Halperin et al. disclose a similar vest which is similarly not portable.
Lach et al., in U.S. Pat. No. 4,770,164, disclose a circumferential band and take-up reel used to generate a rise in thoracic pressure. Although either manually or mechanically driven, this apparatus requires the use of a backboard for guiding the band around the chest.
The use of bands or belts to generate a rise in intrathoracic compression for the purpose of assisting respiratory ailments is disclosed in U.S. Pat. No. 651,962 to Boghean. This device is for periodic loosening and tightening of the band around a patient's chest for treating respiratory disease by regulating periods of breathing as well as the size or depth of breath.
In U.S. Pat. No. 3,777,744, Fryfogle et al. disclose a breathing aid consisting of a belt and a handle which tightens the belt for expelling excessive residual air in the lungs.
Other devices known to the Applicants using circumferential bands for generating a compression force on the abdomen and lower chest to assist in compression of lungs for respiratory purposes include U.S. Pat. No. 2,899,955 to Huxley, U.S. Pat. No. 3,368,581 to Glascock and U.S. Pat. No. 2,754,817 to Nemeth. Furthermore, the use of inflatable bladders positioned around either the chest or the abdomen have been disclosed in U.S. Pat. No. 3,481,327 to Drennen, U.S. Pat. No. 3,120,228 to Huxley, U.S. Pat. No. 3,042,024 to Mendelson, U.S. Pat. No. 2,853,998 to Emerson, U.S. Pat. No. 2,780,222 to Polzin, U.S. Pat. No. 2,071,215 to Petersen, U.S. Pat. No. 4,424,806 to Newman and U.S. Pat. No. 4,928,674 to Halperin.
U.S. Pat. No. 2,699,163 to Engstrbm, shows a respirator device for ventilating a patient's lungs.
U.S. Pat. No. 5,295,481 to Geeham shows a chest compression device comprising a T-shaped mechanical chest compression apparatus with a suction cup. The central shaft attached to the cup may be compressed beyond the lips of the cup and bruise or otherwise injure the patient due to the concentration of force on the patient by the shaft tip.
U.S. Pat. Nos. 4,397,306 to Weisfeldt et al. and 1,399,034 to Taplin show large mechanical devices for compressing the chest of a cardiac arrest patient.
Szpur, in U.S. Pat. No. 5,407,418, discloses a power-driven, pulsating compressor apparatus for stimulating blood flow within vessels of a person's foot or hand. The device periodically applies a concentrated force against a localized region of the foot or hand.
In spite of the prior art, the need still exists for a device which effectively increases the flow of blood in the organs of a cardiac arrest patient. This device should be truly portable and useable by a person of average strength and skill.